1. Field of the Invention
The present invention relates to a novel chemical vapor deposition (CVD) process for depositing sp.sup.3 -bonded diamond-type carbon films via a non-electrically driven radiant energy source. More specifically, the present invention relates to the use of a concentrated solar flux directed through a volatile hydrocarbon gas/H.sub.2 reactant mixture to produce temperature ranges on a substrate of approximately 750.degree. C.-950.degree. C. at pressures of 1 to 50 Torr in a specialized cold wall vacuum/CVD chamber to produce sp.sup.3 -bonded diamond-type carbon on the substrate.
2. Description of the Prior Art
The development of CVD processes to produce a carbon coating with the intrinsic properties of diamond has been a subject of considerable interest and investigation in the scientific community, since synthetic amorphous and crystalline diamond-type materials provide an unusual combination of properties such as high values of hardness, density, refractive index, transparency, chemical/electronic resistance and thermal conductivity.
However, except for the acetylene torch method, conventional options for the CVD processing of diamond (and even non-diamond materials) all have one common drawback; namely, they require electrically-generated thermal or photolytic activation to produce a product. These energy-intensive electrical processes entail the use of inefficient multiple conversions of energy resources such as: primary resource (fossil fuels or nuclear material) to heat; heat to electricity; and the use of electricity back to heat or radiant energy.
In prior art processes, energy losses at each conversion step were either ignored, tolerated, or accepted due to the erroneous prevailing view that the economy of the whole process was based on cheap and limitless energy resources. Moreover, the environmental liability or hazards utilizing the additional consumption of fossil fuels or nuclear material to support this energy waste appears not to have been seriously considered.
For example, in U.S. Pat. No. 4,565,618 an apparatus is described that permits diamond-like carbon flakes to be produced by the deposition of carbon from a beam containing carbon ions and atoms onto a smooth surface that is simultaneously ion beam sputtered. The bombarding ions have sufficient energy to create diamond bonds; however, the process in this patent uses a physical vapor deposition process that produces flakes, rather than continuous coatings.
A process for forming a film adhered to a substrate in an evacuated atmosphere is disclosed in U.S. Pat. No. 4,992,298. Essentially, the process describes a method of ballistically alloying a very thin film to a substrate and subsequently depositing a second layer of polycrystalline diamond onto it. This process is somewhat of a variation of the process in U.S. Pat. No. 4,565,618 in that it substitutes a sputter target for the electric arc evaporation. Furthermore, the process of this patent describes a physical vapor deposition (PVD) process and specifically excludes hydrogen from the vacuum chamber.
U.S. Pat. No. 5,055,318 discloses a low-temperature process for forming a stress-reduced film adhered to a substrate in an evacuated atmosphere, comprising: depositing a layer of a desired non-hydrocarbon substance on the substrate with a low energy, sputtered atomic beam; simultaneously exposing the substrate to a first, high energy beam of inert atoms to grow a ballistically alloyed layer of an initial desired thickness; reducing the first, high energy beam to a second, substantially less high energy beam to obtain a film of a final desired thickness on the ballistically alloyed surface of the substrate. This process is a PVD process; it uses expanded energy ranges for the ion beams, and can replace the sputtering ion beam and target with a thermal evaporation source. Nevertheless, the process also specifically excludes hydrogen from the vacuum chamber.
A microwave enhanced CVD method for depositing carbon is described in U.S. Pat. No. 4,869,923, wherein plasma enhanced CVD using electronic cyclotron resonance (ECR) or a modified cyclotron resonance (MCR) at higher pressures is used to grow diamond-thin films; however, the process in this patent must employ a DC magnetic field established in the microwave (2.45 GHz) or radio frequency (13.56 MHz) plasma to induce the ECR or MCR conditions to excite the reactants in gas phase, before impact with the substrate surface. Further, the process of this patent utilizes infrared or halogen lamp radiation to heat the substrates and requires nitrogen gas as a constituent of the precursor stream.
U.S. Pat. No. 5,015,494 uses a cyclotron resonance chemical vapor deposition method to form a diamond or diamond-like carbon material on a substrate by: inputting at least one reactive gas containing carbon in a reaction chamber; emitting a microwave into the reaction chamber at a predetermined frequency and in a predetermined direction; establishing a magnetic field in the reaction chamber where the direction of the magnetic field is parallel to the direction of the microwave and the strength of the magnetic field is such as to cause cyclotron resonance at a predetermined position in the reaction chamber; exhausting the reaction chamber to establish a pressure range of 0.1 to 300 Torr; holding the substrate at the predetermined, cyclotron resonance position in the reaction chamber; and depositing a diamond-like carbon material on a surface of the substrate; however, the process in this patent also requires a DC magnetic field established in a microwave or radio frequency plasma to induce the ECR or MCR conditions to excite the reactants in the gas phase before impact with the substrate surface. The process in this patent is similar to that in U.S. Pat. No. 4,869,923 in that it utilizes infrared or halogen lamp radiation to heat the substrates from the backside when required, and requires nitrogen gas as a constituent of its precursor stream.